The present invention relates to a composite material having sliding property which is produced by applying, to a substrate, a fluorine-containing polymer excellent in sliding property, non-sticking property, heat resistance, transparency (property for exhibiting clear surface pattern), water- and oil-repellency and particularly adhesive property to the substrate and utilizes particularly sliding property thereof.
Hitherto with respect to a heating surface of, for example, an iron in the field of domestic appliances, not only excellent heat resistance but also excellent sliding properties such as friction resistance and abrasion resistance have been demanded since it is used while being pressed onto clothes and slid thereon. Namely a material being excellent in sliding properties is required to be applied to such a portion.
As a material having sliding properties, generally there are engineering plastics such as polyacetal and PPS, silicon material and fluorine-containing material, particularly a fluorine-containing resin which are common materials and have been used practically.
However, there is a substantial problem that the fluorine-containing resin is insufficient in adhesion to a substrate of metal or glass due to its excellent non-sticking property.
Therefore in case where the fluorine-containing polymer is used in the form of a coating, there is a method of adhering a fluorine-containing resin to a substrate by roughening the surface of metal chemically or physically with expecting anchor effect between them. However this method requires much labor in the surface roughening itself, and though initial adhesion is possible, lowering of the anchor effect arises when a temperature change is made repeatedly and in case of use at high temperature.
Also a method for chemically activating a surface of a fluorine-containing resin by treating the surface with a solution prepared by dissolving metallic sodium in liquid ammonia has been proposed. However in that method, not only there is a fear that the solution itself causes environmental pollution but also there is a problem that its handling is attended with danger.
Further though a method for carrying out physical and chemical treatment such as plasma sputtering on a surface of a fluorine-containing resin has been proposed for activation of the resin surface, there is a problem that much labor is required for the treatment and an increase in cost is resulted.
Also in order to improve adhesion of a fluorine-containing resin coating, investigations with respect to addition of various components and formation of a primer layer have been made.
For example, there is a technique of adding an inorganic acid such as chromic acid to a coating composition containing a fluorine-containing polymer to form chemical conversion coating film on a surface of metal for enhancing adhesion of the composition (JP-B-63-2675). However since chromic acid contains hexahydric chromium, it cannot be said that such a technique is sufficient in view of safety in food and coating work. Further in case of use of other inorganic acids such as phosphoric acid, there was a problem that safety of a fluorine-containing resin coating composition is damaged.
Use of a coating composition containing a fluorine-containing resin as a primer, in which heat resistant resins such as polyamide imide, polyimide, polyethersulfone and polyether ether ketone and in addition, a metal powder are added instead of the above-mentioned inorganic acid, has been studied (JP-A-6-264000). Inherently there is almost no compatibility between a fluorine-containing polymer and a heat resistant resin. Therefore there arises a phase separation in a coating film, thus easily causing intercoat adhesion failure between the primer and the top coat of the fluorine-containing resin. Further film defects such as pin holes and cracks arise easily at the time of processing at high temperature or during use due to a difference in heat shrinkage between the fluorine-containing resin and the heat resistant resin or due to lowering of elongation of the coating film by the addition of the heat resistant resin. Also since those heat resistant resins are colored brown by baking, property for exhibiting clear surface pattern is poor and it is difficult to use them for applications requiring white and vivid colors and transparency. Further when the heat resistant resin is blended, non-sticking property and friction resistance which the fluorine-containing polymer inherently possesses are lowered.
Also for adhesion of a fluorine-containing resin coating composition to a glass, etc. requiring transparency, an improvement of the adhesion has been tried by treating the substrate with a silane coupling agent or adding a silicone resin to the fluorine-containing resin coating composition (JP-B-54-42366, JP-A-5-177768). However enhancement of adhesion is insufficient, heat resistance is lowered and separation of a coating film, foaming and coloring arise easily at sintering or in use at high temperature.
On the contrary, fluorine-containing resin coating compositions prepared by copolymerizing a hydrocarbon monomer (containing no fluorine) containing functional group such as hydroxyl or carboxyl have been discussed. However since those coating compositions were originally studied mainly for a purpose of weather resistance, sliding properties (particularly friction resistance) directed by the present invention are insufficient and it is difficult to use them for application requiring heat resistance (for example, 200xc2x0 to 350xc2x0 C.).
Namely with respect to a polymer prepared by copolymerizing a hydrocarbon monomer (containing no fluorine) having functional group, thermal decomposition easily occurs on components of the monomer at the time of processing at high temperature or during use, and thus coating film failure, coloring, foaming, separation, etc. arise, which makes it impossible to attain purposes of coating a fluorine-containing resin.
Further fluorine-containing polymers are generally insufficient in mechanical strength and dimensional stability, and high in price. In order to minimize those disadvantages and make the best use of the above-mentioned merits which the fluorine-containing polymer possesses inherently, investigations have been made also with respect to its use in the form of film.
However the fluorine-containing polymer inherently has low adhesive force, and it is difficult to adhere the fluorine-containing polymer in the form of film directly to other material (substrate). For example, even if the adhering is tried by thermo-processing, adhesive strength of the fluorine-containing polymer is not enough, or even if the polymer has adhesive force to a certain extent, such an adhesive force is apt to vary depending on kind of the substrate. Thus in many cases, reliability on the adhesive strength of the fluorine-containing polymer has been not so enough.
In order to adhere the fluorine-containing polymer film to a substrate, mainly the following methods have been studied:
1. a method for physically roughening a surface of substrate by sand blasting, etc.,
2. a method for surface-treating a fluorine-containing resin film by chemical treatment such as sodium etching, plasma treatment, photochemical treatment, etc.,
3. a method for adhering by using an adhesive, and other methods. With respect to the methods 1 and 2 above, other steps are required, and the steps are complicated and productivity is poor. Also kinds and shapes of substrates are restricted. Further the obtained adhesive force is insufficient, and also there easily occur a problem with appearance (property for exhibiting clear surface pattern) of the obtained composite materials such as coloring and color. Also the method of using a chemical such as sodium etching has a problem with safety.
Use of an adhesive in the method 3 above has also been discussed. A usual hydrocarbon type (containing no fluorine) adhesive does not have enough adhesive property and its heat resistance is insufficient. Thus a hydrocarbon type adhesive cannot stand under conditions for adhering of a fluorine-containing polymer film which requires molding and processing at high temperature, and peeling due to decomposition of the adhesive and coloring occur. Since the above-mentioned laminated article produced by using an adhesive also is insufficient in heat resistance, chemical resistance and water resistance, it cannot maintain adhesive force due to a change in temperature and environment, and lacks in reliability.
On the contrary, adhesion by using an adhesive composition comprising a fluorine-containing polymer having functional group is discussed.
For example, it is reported that a fluorine-containing polymer prepared by graft-polymerizing, to the fluorine-containing polymer, a hydrocarbon monomer which has carboxyl represented by maleic anhydride and vinyltrimethoxysilane, a residual group of carbonic acid, epoxy or a hydrolyzable silyl group, is used as an adhesive (for example, JP-A-7-18035, JP-A-7-25952, JP-A-7-25954, JP-A-7-173230, JP-A-7-173446, JP-A-7-173447) and that an adhesive composition comprising a fluorine-containing copolymer prepared by copolymerizing a hydrocarbon monomer having functional group such as hydroxyalkyl vinyl ether with tetrafluoroethylene or chlorotrifluoroethylene and an isocyanate hardening agent is cured and used as an adhesive between vinyl chloride resin and corona-discharged ETFE (for example, JP-A-7-228848).
The above-mentioned adhesive composition comprising a fluorine-containing resin prepared by graft-polymerizing or copolymerizing a hydrocarbon monomer having functional group does not have enough heat resistance, and thus at the time of processing a composite material comprising the adhesive composition and a fluorine-containing resin film at high temperature or during use at high temperature, decomposition and foaming occur, thereby causing reduction of adhesive strength, peeling and coloring. In case of the adhesive composition disclosed in JP-A-7-228848, it is necessary to corona-discharge the fluorine-containing resin film.
As mentioned above, no composite materials having sliding properties which assure strong adhesion to a substrate have been obtained.
In view of the above-mentioned facts, an object of the present invention is to provide composite materials having sliding properties (friction resistance) which are produced by applying, to a substrate, a material comprising a fluorine-containing polymer being excellent in adhesion to the substrate without necessitating complicated steps.
Further an object of the present invention is to obtain the composite materials having sliding properties excellent in stain-proofing property, non-sticking property, transparency (property for exhibiting clear surface pattern), anti-bacterial property, water- and oil-repellency, stain removable property, chemical resistance, rust-preventing property and resistance to energy rays.
The present invention relates to a composite material having sliding properties which is produced by applying, to a substrate, a material comprising a fluorine-containing ethylenic polymer having functional group and prepared by copolymerizing:
(a) 0.05 to 30% by mole of at least one of fluorine-containing ethylenic monomers having at least one functional group selected from the group consisting of hydroxyl, carboxyl, a carboxylic salt group, a carboxylic ester group and epoxy and
(b) 70 to 99.95% by mole of at least one of fluorine-containing ethylenic monomers having no functional group mentioned above.
In that case, it is preferable that the above-mentioned fluorine-containing ethylenic monomer (a) having functional group is at least one of fluorine-containing ethylenic monomers represented by the formula (1):
CX2xe2x95x90CX1xe2x80x94Rfxe2x80x94Yxe2x80x83xe2x80x83(1)
wherein Y is xe2x80x94CH2OH, xe2x80x94COOH, a carboxylic salt group, a carboxylic ester group or epoxy, X and X1 are the same or different and each is hydrogen atom or fluorine atom, Rf is a divalent fluorine-containing alkylene group having 1 to 40 carbon atoms, a fluorine-containing oxyalkylene group having 1 to 40 carbon atoms, a fluorine-containing alkylene group having ether bond and 1 to 40 carbon atoms or a fluorine-containing oxyalkylene group having ether bond and 1 to 40 carbon atoms.
Further it is preferable that the fluorine-containing ethylenic monomer (b) having no functional group mentioned above is tetrafluoroethylene.
Further it is preferable that the fluorine-containing ethylenic monomer (b) having no functional group mentioned above is a monomer mixture of 85 to 99.7% by mole of tetrafluoroethylene and 0.3 to 15% by mole of a monomer represented by the formula (2):
xe2x80x83CF2xe2x95x90CFxe2x80x94Rf1xe2x80x83xe2x80x83(2)
wherein Rf1 is CF3 or ORf2, in which Rf2 is a perfluoroalkyl group having 1 to 5 carbon atoms.
In the present invention, it is preferable that the fluorine-containing ethylenic polymer having functional group is applied to a substrate in the form of a coating composition, an aqueous dispersion, a powder coating or a film.
The substrate may be a metallic substrate, a ceramic substrate of glass or porcelain or a synthetic resin substrate.